Computer Analysis of Spectra of Enzyme-Substrate and Enzyme-Inhibitor Complexes Involving Aspartate Aminotransferase

Dicarboxylic acid inhibitors and the amino and keto acid substrates interact with aspartate aminotransferase (EC 2.6.1.1) to form spectrally distinct enzyme-inhibitor and enzyme-substrate complexes. The spectra of solutions of the enzyme and varying concentrations of inhibitor or substrate are analyzed by computer methods to obtain the spectra of the enzyme-inhibitor and enzyme-substrate complexes. Programs have been written which permit the computation of the pKa values and the dissociation constants of the complexes with the use of the spectral data at many wave lengths. The complete spectra of the individual ionic species of the complexes are drawn. Comparison plots of the experimental spectral data and the calculated spectra can also be obtained. These computer methods are applied to four enzyme-inhibitor complexes and to complexes of the enzyme with its substrates and two pseudosubstrates. Spectra of apoaspartate aminotransferase containing bound pyridoxal phosphate analogues have also been analyzed.